1. Field of the Invention
The present invention relates to a method of preparing a carbon dioxide adsorbent, an adsorbent prepared thereby and a carbon dioxide capture module containing the adsorbent.
2. Discussion of Related Art
Carbon dioxide generated by the combustion of a fossil fuel is the main greenhouse gas generated as the result of an industrial activity. The generated carbon dioxide accumulated in the air increases an average temperature, and thus causes a climate change. As long as an energy efficient alternative that does not emit a greenhouse gas is not developed, a fossil fuel will be continuously consumed, and the concentration of carbon dioxide will gradually increase. Accordingly, controlling the emissions of carbon dioxide and a technique of capturing carbon dioxide will become the most important environmental issue in the world.
A technique of capturing carbon dioxide and a technique of storing the captured carbon dioxide in oceans or geological materials are collectively called carbon capture and storage (CCS). CCS comes to the fore as a solution for reducing the concentration of carbon dioxide. Recently, many studies focused on the removal of carbon dioxide such as cryogenic fractionation, membrane separation, solvent absorption, and physical and chemical sorption with respect to a solid surface have been reported. Cryogenic fractionation has a disadvantage of high energy consumption to remove carbon dioxide in a flue gas. Membrane separation is effective and already used to separate carbon dioxide, but it is difficult to be used throughout a wide range of industrial fields due to a complicated method and a high cost. Currently, solvent absorption is performed using various solvents. Particularly, the solvent absorption based on an amine is already commercially used. However, since a process of absorbing carbon dioxide and regenerating a solvent needs a lower pressure and temperature (40 to 150° C.), an additional process of decreasing a temperature of a flue gas in an industrial process operated at intermediate and high temperatures is needed. While temperatures of a gas input into a turbine and a flue gas of general processes, in addition to an integrated gasification combined cycle (IGCC), are generally in an intermediate temperature range of 150 to 450° C., so far, most adsorption and capture studies have been performed at a low temperature of 100° C. or less. Accordingly, to apply an adsorption process adjusted to a low temperature, an additional process of decreasing the temperature of the gas should be introduced, and therefore, a process operating cost increases. If a solid adsorbent capable of effectively capturing carbon dioxide in the intermediate temperature range is developed, carbon dioxide can be removed without a process of decreasing the temperature of an exhaust gas, and therefore, the process operating cost can be reduced.
Currently, a metal oxide adsorbent being actively studied is known to adsorb carbon dioxide from a low temperature to a high temperature. Particularly, a study on the metal oxide adsorbent based on an alkali metal and an alkali earth metal is progressing in consideration of an adsorbed amount of carbon dioxide and regeneration efficiency. An adsorbent based on lithium, Li4SiO4, may adsorb a large amount of carbon dioxide, but needs a desorption process at a high temperature (700 to 900° C.) to regenerate the used adsorbent [CO2 capture system using lithium silicate for distributed power supply, Energy Procedia 37 (2013) 1194-1201]. Adsorbents based on Ca perform adsorption at 600 to 700° C., but a high temperature of 800° C. or more is needed for desorption. Even though having excellent adsorbability, an adsorbent having high energy consumption is difficult to be applied commercially in the desorption process for regeneration [Separation of methane from CH4/CO2/N2 mixed gases using PSA method, CLEAN TECHNOLOGY, Vol. 17, No. 4, December 2011, pp. 389˜394]. Accordingly, in addition to excellent adsorbability, detachment efficiency is also an important consideration to select an adsorbent.
Among various metal oxides, magnesium oxide is a material which is being studied in various ways as a dry adsorbent. Magnesium oxide which facilitates the adsorption of carbon dioxide in the temperature range of the flue gas and can be regenerated at a relatively low temperature is highly valued as a dry adsorbent for carbon dioxide. The MgO-based adsorbent capable of capturing carbon dioxide can be made by processing dolomite at 300 to 450° C. and 20 atm.
In conventional methods of processing an MgO synthesis product, there are precipitation methods [Roles of double salt formation and NaNO3 in Na2CO3-promoted MgO absorbent for intermediate temperature CO2 removal, International Journal of Greenhouse Gas Control 12 (2013) 351-358; Advanced adsorbents based on MgO and K2CO3 for capture of CO2 at elevated temperatures, International Journal of Greenhouse Gas Control 5 (2011) 634-639] and simple mixing methods [Roles of double salt formation and NaNO3 in Na2CO3-promoted MgO absorbent for intermediate temperature CO2 removal, International Journal of Greenhouse Gas Control 12 (2013) 351-358; Fabrication of a new MgO/C sorbent for CO2 capture at elevated temperature, J. Mater. Chem. A, 2013, 1, 12919-12925]. In the precipitation methods, water is used as a solvent, and a product and the solvent are separated using a filter after a reaction. However, due to the use of a filter, salts used to synthesize MgO pass through a filter in an ion state and thus are lost. Simple mixing is a method of physically mixing powders which become the materials of a synthesized MgO compound, and even though it is simple, there is a disadvantage in that it is difficult to obtain a uniform synthesized product due to a low degree of dispersion.